In the next decade the upgrades of the Auger and TA observatories can contribute answering these questions [1]}, [2]}. Yet, to reach this goal, it is necessary to refine both experimental analysis and theoretical understandings. Mass determination is currently limited by the uncertainties in the predictions of hadronic models and muon content in the EAS, the planned Auger upgrade with an independent measurement of the electromagnetic and muonic content of the EAS could help solve this problem. Precise mass determination till the highest energies will be of paramount importance in the future. The necessary step forward should be disentangling the all-particle energy spectrum into that of individual mass groups (as for instance p, He, CNO, MgAlSi, Fe). On more general grounds, the clearest path to event-by-event primary mass reconstruction lies in a high-resolution independent reconstruction of both \(X_{max}\)  and muon content coupled to a high-resolution energy measurement.
